1. Field of the Invention
The present invention relates to a sheet processing device which flattens down a folded back portion of a folded and curved sheet bundle, and an image formation apparatus incorporating this device. In particular, the present invention relates to a sheet processing device which flattens down the folded back portion of the sheet bundle, the sheet processing device including a function for sending the sheet bundle through a gripping roller pair and a function for gripping the sheet bundle when flattening down the folded back portion of the sheet bundle with a pressing unit, and to an image formation apparatus.
2. Description of the Related Art
Conventionally, sheets of a predetermined number (e.g., around twenty) are stacked and folded into booklet-like form with stitching/folding equipment. The sheet bundles that are folded down with such stitching/folding equipment include sheet bundles that are simply folded, sheet bundles that are saddle-stitched and folded, sheet bundles that are not bound with string or staples but are glued (perfect binding) and folded, and so forth.
However, all types of sheet bundles possess some degree of resilience, and accordingly, following folding, the area of the curved folded back portion (folded tip portion, back cover) bulges and bends and forms a U-shape, and tends to form a small opening on the open side of the folded sheet bundle. Such sheet bundles become unstable when bundled and collapse easily, and storage and conveying of such sheet bundles have been troublesome.
To solve this problem so that the folded sheet bundles can be placed flat, a folded back flattening processing device that flattens down the folded back portion of the folded sheet bundles is known (see U.S. Pat. No. 6,692,208).
As illustrated as an example in FIG. 17, a conventional folded back flattening processing device 901 is integrated into a sheet processing device 920. Further, the sheet processing device 920 is connected to a main device unit 922 of a photocopier 921 (image formation apparatus). The photocopier 921 forms images on the sheets. This conventional sheet processing device 920 forms booklet-like sheet bundles as illustrated in FIGS. 17 and 20.
The sheet processing device 920 receives and makes bundles S with a saddle tray 960 from sheets that are sent in order and having an image formed by the main device unit 922. The center of the sheet bundle is bound with a stapler 962. Then, the sheet bundle is conveyed in the lower direction, and is received and stopped by a stopper 963. After this, an abutting plate 961 abuts the bound portion of the sheet bundle, and presses the sheet bundle into a nip portion of a folding roller pair 907. The folding roller pair 907 folds the sheet bundle with the nip portion while discharging the sheet bundle to a discharge belt pair 906. The folded sheet bundle S is conveyed in the direction of arrow B with the folded back portion Sb at the leading edge, by the discharge belt pair 906, and is sent through one pair of separated gripping members 902 and 903 (FIG. 19A). Then the folded back portion Sb of the sheet bundle S is received by a stopping plate 905 and stops. The discharge belt pair 906 then stops conveying the sheet bundle, and the pair of gripping members 902 and 903 grip the sheet bundle. At this time, the folded back portion Sb protrudes from the gripping members 902 and 903.
After this, the stopping plate 905 rises and separates from the folded back portion Sb (FIG. 19B). Then, a pressing roller 904 runs along the folded back portion Sb in the direction of the arrow A while pressing the folded back portion Sb, and flattens down the curved folded back portion Sb (FIGS. 18, 19B, and 20). Finally, the discharge belt pair 906 discharges the processed sheet bundle S onto a discharge sheet tray 908 (FIG. 19C).
As described above, the gripping members 902 and 903 of the conventional sheet processing device 920 only functions to grip the sheet bundle S.
Thus, the conventional sheet processing device 920 have the gripping members 902 and 903 which only function to grip the sheet bundle S, therefore necessitating the discharge belt pair 906 as a sheet conveying device for discharging the sheet bundle from the gripping members 902 and 903, increasing the size and complexity of the configuration of the device. This further has led to increased overall size of the image formation apparatus having such a sheet conveying device.